1. Field of the Invention
The present invention relates to a photoconductor for electrophotography to be used for forming images by an electrophotographic process such as a copying machine, a printer, a facsimile, etc., and a method of manufacturing the photoconductor.
2. Description of the Related Art
In an image producing system employing a photoconductor for electrophotography, firstly electricity is charged on the surface of a photoconducting photosensitive medium as by corona charge and then an electrostatic latent image is formed by light exposure, whereupon the latent image is developed with toner as a visible image. The common problem with the photoconductor for electrophotography of this image producing system is that the photosensitive medium is locally unevenly charged due to, for example, its surface defects, often causing a remarkable image fault such as black spot and fog. For many of various possible causes for such local uneven charging, electric charges are introduced locally between an electrically conductive support and a photoconductive layer. For most of conventional conductive supports, aluminum or an alloy containing chiefly aluminum is used as a substrate, and a blocking layer is disposed between such aluminum substrate and the photoconductive layer in an attempt to eliminate the above-mentioned problem.
This conventional blocking layer is exemplified by a resin layer as of polyamide, polyimide, polyvinyl alcohol, polyurethane, casein or cellulose, and an inorganic layer as of aluminum oxide or aluminum hydroxide. Although the inorganic layer, i.e., the anodic oxidation film itself is a pit-free homogeneous covering film, its uniformity depends on the composition of the substrate because aluminum ions are consumed during the anode oxidation. With the substrate partly crystallized, its surface would become uneven due to dents called pits not only giving a bad influence on formation of the photoconductive layer but causing the image fault.
For the aluminum alloy to be used as the conductive support, usually a small quantity of magnesium (Mg), silicon (Si), copper (Cu) and titanium (Ti) is added in order to secure a constant degree of mechanical strength, and additionally impurities such as iron (Fe) and manganese (Mn) are contained as they originate from the aluminum ingot. These metal elements are crystallized to form local lumps while the aluminum alloy is cast into a tubular substrate. Since they are different in chemical property from aluminum, these crystalline lumps dissolve earlier than aluminum during anode oxidation so that the crystalline lumps near the substrate surface would be removed off to cause pits.
Attempts have been proposed by, for example, Japanese Patent Laid-Open Publications Nos. Sho59-193463 and Hei7-319194, to solve the foregoing problem. Japanese Patent Laid-Open Publication No. Sho59-193463 discloses a technique of regulating the impurity content of iron (Fe) to 2000 ppm or less (a metal of 99.8 or more % by weight) in an effort to avoid above-mentioned faults in a photoconductive layer. Japanese Patent Laid-Open Publication No. Hei7-319194 discloses a technique of controlling electrolytic conditions during anode oxidation to reduce the above-mentioned faults in a photoconductive layer.
However, in the first-named conventional technique, the faults such as pits cannot be prevented even if a high-purity aluminum alloy is used. Also in the second-named conventional technique, the already crystallized lumps cannot be prevented from becoming deteriorated during formation of the aluminum alloy tube. According to these conventional techniques, partly since a high-purity aluminum alloy is used and partly since it is necessary to rectify current with high precision, it would inevitably result in an increased cost of production.
Therefore with the blocking layer using either the anodic oxidation film or the polymer resin, which is obtained by either conventional technique, it would be difficult to eliminate image defects such as black spots and fog, particularly occurrence of fog would be remarkable in a high-temperature and high-humidity environment.
Further, in the method employing the anodic oxidation film, partly since the blocking effect tends to fluctuate and partly since the heat resistance is poor, the substrate would be cracked in its surface while being dried, thus causing the uneven coating during formation of the photoconductive layer and lowering insulator-destruction strength so that the crack can grow into the photoconductive layer.